I. Infectious Bovine Rhinotracheitis
Bovine herpesvirus type 1 (hereinafter "BHV-1"), more commonly known as infectious bovine rhinotracheitis virus (hereinafter "IBRV"), has been associated with respiratory, reproductive, enteric, ocular, central nervous system, neonatal, mammary, and dermal infections of cattle (Gibbs, E. P. J. et al, Vet. Bull. (London), 47: 317-313 (1977)). Evidence for the association of IBRV with diseases of the respiratory tract was first obtained in the early 1950's. It has since become apparent that infectious bovine rhinotracheitis (hereinafter "IBR") has a worldwide distribution. By the mid-1960's, respiratory disease caused by IBRV resulted in losses in the United States estimated at about $25 million. Additional losses associated with IBRV infections have been due to abortion storms, dramatic losses in milk yield, metritis, enteritis, and meningitis. Since 1972, more severe forms of IBRV respiratory infections have become widespread in Canada and Western Europe. New IBR outbreaks probably result from exposure to imported asymptomatic IBRV carriers or exposure to infected animals prior to the onset of clinical disease. Hence, the importation of IBRV-infected livestock may be restricted or forbidden by some countries.
The spread of IBR in naturally and artificially bred cattle also poses a serious problem, espeically with the continued, widespread use of frozen semen. In addition, recurrent shedding of IBRV from infected bulls constitutes a significant threat to the artificial insemination industry in the United States and to the worldwide distribution of bovine germ plasm. The incrimination of IBRV as the etiologic agent of oophoritis and salpingitis with resultant infertility and sterility adds to the seriousness of IBRV infections.
Natural IBRV infections of species other than cattle occur in swine, goats, water buffalo, wildebeasts, ferrets, and mink. Experimental infections have been established in swine, goats, mule deer, ferrets and rabbits (Joo, H. S. et al, Am. J. Vet. Med. Assoc., 45: 1924-1927 (1984)).
The severity of illness resulting from IBRV infections depends upon the virus strain and on the age of the animal affected. After recovery from infection, animals may show clinical signs of recurrent disease without being reexposed to the virus. Recurrent disease without reexposure occurs because the virus remains dormant, i.e., latent, in neurons of the sensory ganglia of its host and can be reactivated, even after long periods (Rock, D. L. et al, J. Gen. Virol., 67: 2515-2520 (1986)). Dexamethasone treatment can also provoke nasal shedding of the virus with or without clinical symptoms of active IBR. This suggests that reactivation and release from neuronal sites and, possible, persistent infection of other tissues can occur (Rossi, C. R. et al, Am. J. Vet. Res., 43: 1440-1442 (1982)). Reactivation of IBRV from latency and symptomatic shedding can also occur spontaneously so that cattle latently infected with field strains of IBRV represent a sporadic source of virus transmission and herd infection.